Analysis and design of linear-to-circular polarising reflector antennas exploiting periodic metallodielectric arrays
Mercader Pellicer, Salvador
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This thesis presents an eﬃcient way to analyse and design linear-to-circular polarising reﬂector antennas comprising doubly periodic metallodielectric arrays. These type of structures, used in conjunction with subreﬂectors, has risen as a promising solution to reduce the number of reﬂectors in multi-beam antennas in single-feed-per beam architectures while providing circular polarisation for the downlink/uplink. The ﬁrst part of the thesis is concerned with the analysis of single reﬂector antennas, focusing on their depolarisation properties. MATLAB® codes are developed to obtain the far-ﬁeld from the reﬂector and are successfully compared against the preferred tool in the market for the analysis and design of reﬂector antennas, i.e.,TICRA’s GRASP. This analysis tool is used in conjunction with a Floquet analysis of periodic structures to obtain the far-ﬁeld from doubly periodic metallodielectric arrays. An efﬁcient way to extract the fundamental modes from the near-ﬁeld of the feed is introduced for cases where the the reﬂector is placed at the near-ﬁeld of the feed. A design procedure to reduce the cross-polarisation of the polarising reﬂector far-ﬁeld is included. This procedure is based on physical insight rather than brute-force optimisation, leading to computational eﬃciencies. Design examples are shown are compared against the original uniform unit-cell array design. Improvements up to 16 dB in the cross-polarisation levels across a wide bandwidth are achieved. The procedure is validated experimentally. The design procedure is also applied to a multi-beam case where three ideal sources are used to feed the reﬂector. Compared with the uniform unit-cell array, improvements up to 10 dB are obtained in the cross-polarisation performance for the whole bandwidth and the three feeds at the same time.